Perimeter independent precision locating member for a semiconductor chip and method of making said member

Abstract: A perimeter independent precision locating member (22) for a semiconductor chip (10) for ensuring that contact sites (20) upon the chip will be reliably positioned relative to connection members (18), such as contacts or leads, so that the chip can be electrically engageable. The locating member (22) is disposed upon the surface of the semiconductor chip (10) at a specific position relative the contact sites within the perimeter (24) of the chip and being closely matable with a complementary portion of a housing (12) that contains the connection members (18). The method of making the perimeter independent precision locating member (22) for a semiconductor chip (10) involves coating the chip with a layer of photocurable material, masking the material in relation to the contact sites so that the portion of the material that will become the locating member (22) is exposed, illuminating the exposed portion of the photocurable material, and stripping from the chip the uncured portion to define the locating member (22).

Description: This invention relates to the positioning of contact sites of a semiconductor chip to their respective connection members in order to assure electrical connection with the semiconductor chip. Semiconductor chips, or chip(s), provide complex electrical functions in small packages and are fabricated as part of a larger semiconductor wafer. The individual semiconductor chips are separated from the semiconductor wafer by an operation called "dicing" where the chip is cut along what becomes its peripheral edge. The chips are most familiar in electronic applications, such as microprocessors, but may also be useful as electro-optic devices, for example lasers and light emitting diodes. The semiconductor wafers are processed through conventional techniques of etching, diffusing and doping to produce the desired functions of the individual chips. Each individual chip has a plurality of contact sites exposed along a major surface of the chip that will become engaged by connection members of another electrical article, such as leads or contacts in a socket, to form electrical connections with the chip. The connection members are prepositioned in the article in an arrangement that corresponds to the contact sites of the chip and then the chip must be positioned so that the contact sites and the connection members correspond during its assembly to the article. If the contact sites are large relative to the connection members, there is sufficient positioning tolerance available so that the peripheral edges of the chip may be utilized to position the chip. One way of doing so is to create a recess that is located relative to the connection members, so that when the chip is within the recess in the article the contact sites align with the connection members. If the periphery of the chip produced during dicing is undersized, the chip may float within the recess. The greater the dimensional discrepancy, the greater the float, possibly enough so that proper electrical connection may not be reliably established. Another way of aligning the chip within a recess is described in U.S. Patent Application No. 08/092,149 filed on July 15, 1993. The recess has two adjacent spring sides which bias the chip against opposite sides that are precisely located relative to the connection members. This configuration accommodates variations in the size of the chip while preventing the chip from floating. However, when the periphery of the chip is formed during dicing operation, the edges may still have enough dimensional variation, relative to the contact sites, that the connection members and contact sites may not align accurately enough for reliable electrical engagement. The smaller contact sites associated with the latest chip configurations require extremely accurate placement of contact sites relative to the connection members to assure that proper electrical connections occur. The use of the periphery of the chip, as established during production dicing operations, is no longer adequate. One way of overcoming this difficulty is through the use of a computer controlled positioning system that uses interactive vision capability to acquire the images of both the contact pads and the leads and, by correlating those images, properly position the contact sites relative to the connection members. Unfortunately, these systems are expensive and relatively slow, thereby making them impractical for production operations where large quantities of chips must be individually positioned relative to a fixed arrangement of connection members. As semiconductor chips are becoming a more integral component of electronic devices, and with the advent of multi-chip module technology where numerous semiconductor chips are incorporated into a single module, it is critical that the chips be individually burned-in and tested prior to final assembly. By providing "known good die" or tested semiconductor chips for final assembly, the yield of acceptable devices may be substantially increased. Therefore, the chips must be processed through burn-in within test sockets prior to final assembly into a chip carrier, multi-chip module or other device. This requires the chip to be mated with connection members at least twice -- once for testing or burn-in and again for final assembly. To assure efficient placement of the semiconductor chip, what is needed is a simple, economical and practical means for reliably and precisely positioning the contact sites of a semiconductor chip to mating connection members, such as contacts of a burn-in or test socket or any other device that utilizes a bare chip, whereby positioning the chip assures electrical connection. It is an object of this invention to provide on a semiconductor chip an economical and reliable locating member to assure contact sites of the chip are accurately positioned so that the chip may be electrically engaged. It is another object of this invention to provide an economical way of manufacturing the locating member. According to one aspect thereof the present invention consists in a semiconductor chip as defined in claim 1. EP-A-312 217 and EP-A-439 134 disclose a semiconductor chip according to the preamble of claim 1. US-A-4 565 314 discloses the additional subject matter of claim 2. Alternative shapes of locating members are disclosed in EP-A-312 217, EP-A-439 134, US-A-4 565 314 and JP-A-58125853. According to another aspect thereof the present invention consists in a method, as defined in claim 4, of making a perimeter independent precision locating member for a semiconductor chip. Embodiments of the invention are defined in the subordinate claims. The locating members of a plurality of chips may be simultaneously developed upon the semiconductor wafer before the chips are cut from the semiconductor wafer. The locating member may be formed in an asymmetric shape or off-center to polarize the semiconductor ship, and may comprise two or more locating members asymmetrically located or shaped on each chip. Other objects, features and advantages of the invention will become apparent upon inspection of the following features and the description of the preferred embodiment. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: FIG. 1 is a partially exploded isometric view of a semiconductor chip above a two-piece housing that connects the chip to another electrical device. FIG. 2 is an isometric view of the semiconductor chip showing the contact sites and the locating member. FIG. 3 is an isometric view of an alternative embodiment of the locating member upon the semiconductor chip. FIG. 4 is a top view of a semiconductor wafer showing individual semiconductor chips prior to dicing. FIG. 5 is a cross-sectional view of the semiconductor chip including a passivation layer. FIG. 6 is a cross-sectional view of the semiconductor chip of FIG. 5 with a layer of photocurable material thereupon. FIG. 7 is a cross-sectional view of an illuminated semiconductor chip of FIG. 6 with a mask in place. FIG. 8 is a cross-sectional view of the semiconductor chip of FIG. 5 with a locating member formed thereupon. FIG. 1 shows a semiconductor chip (chip) 10, which is representative of an integrated circuit chip although this invention will work with other types of semiconductor chips, and an illustrative housing 12 that could be part of a burn-in or test socket where the chip 10 must be removable. The chip 10 is held in place, and electrical connection is maintained, by a force acting along Arrow A which is generated by conventional means, such as a top plate or clamps (not shown). The housing 12 is constructed from an upper frame 14 and a lower support 16. The housing 12 includes connection members 18 which electrically connect the chip 10 to an electronic device (not shown). The chip 10 has contact sites 20 that enable the chip 10 to be electrically integrated into the electronic device and a locating member 22 that is precisely positioned upon the chip 10 relative the contact sites 20 independently of the perimeter, or peripheral edge, 24 of the chip 10 (FIG. 2). A complementary portion 26 of the housing 12 is precisely positioned relative to the connection members 18 and mates with the locating member 22 to assure that the contact sites 20 correspond to their respective connection members 18 (FIG. 1). The plurality of connection members 18 are supported in a predetermined arrangement upon the lower support 16 of the housing 12. At one end of each connection member 18 is a foot 28 that is constructed to electrically engage the semiconductor chip 10 at the contact site 20. The connection members 18 gradually diverge outwardly along the face 30 of the lower support 16 to respective terminals 32. The terminals 32 are spaced apart for easy connection to the electronic device through conventional methods, such as a pin contact (not shown) that would fit into a hole 34 in the terminal 32. The lower support 16 may be the dielectric film that supports the connection members 18 of a lead frame used in a chip carrier assembly. The upper frame 14 has an opening 36 sized to approximately correspond to the chip 10 so that the chip 10 may be received therein. The underside 38 of the upper frame 14 has positioning pins 40 that fit within bore holes 42 in the face 30 of the lower support 16 to position the opening 36 generally about the feet 28 of the connection members 18 so that the contact sites 20 of a chip 10 within the opening 36 will be in approximate alignment with their respective feet 28. The upper frame 14 is not a mandatory component of the housing 12 as its primary use, in reference to this invention, is to provide only general positioning of the chip 10. When the size of the contact site 20 approaches the size of the connection member foot 28, it is no longer possible to use the combination of the opening 36 and the perimeter 24 of the chip 10, as established during dicing, for anything more than general positioning. As best seen in FIG. 2, the semiconductor chip 10 would have two opposing first and second major surfaces 44a,44b with the perimeter 24 created during the dicing operation. The contact sites 20 are disposed on one of the first major surface 44a but may be placed on both. Extending outward from the first major surface 44a is the locating member 22, shown in FIG. 2 as a large diameter cylindrical post or boss 46 and a small diameter cylindrical post or boss 48, precisely positioned relative to the contact sites 20. Within the housing 12 is a complementary portion 26 that is precisely positioned relative the feet 28 of the connection members 18 (FIG. 1). The complementary portion 26 is a portion of the lower support 16 that contains two cylindrical recesses 50,52 that are sized to closely receive the corresponding cylindrical posts 46,48 upon the chip, thereby assuring the contact sites 20 correspond to the feet 28 of the connection members 18. The locating member 22 could extend from the second major surface 44b, the surface opposite the one from which the locating member extends in the drawings, and be mated with a part of the housing 12 that would correspond to the second major surface 44b, such as the top plate or clamps that were described above in reference to holding the chip 10 in position. The primary concern is that the complementary portion 26 is precisely positioned relative the feet 28 of the connection members 18 corresponding to the precise position of the locating member 22 relative the contact sites 20. The locating member 22 may also be configured to polarize the chip 10 to assure that the symmetrically arranged contact sites 20 correspond with their respective connection members 18. This is accomplished by configuring the locating member 22 so that it is only receivable by the complementary portion 26 when the chip 10 is properly angularly oriented. The large cylindrical post 46 and the small cylindrical post 48 that make up the locating member 22 assure correct polarization because mating with the complementary portion 26 can only occur when the large cylindrical post 46 corresponds to the large cylindrical recess 50. There are numerous other polarization schemes that are dependent upon basic geometry that would also be useful. For example, the shape of the locating member 22 may be at least partially non-symmetrical in and of itself, such as a trapezoid, or a symmetrical shape could be positioned in a non-symmetrical manner upon the chip 10, such as a symmetrical polygon or circle offset from the chip's axis of symmetry of the chip. Perimeter dependent polarization features, such as the removal of a corner of the chip to assure the chip could only be accepted in a particular orientation, are known. As described above, the present invention does not need perimeter dependent features to provide polarization but their use is not excluded because polarization need not be as accurately maintained as positioning. An alternative embodiment shown in FIG. 3 has the locating member 22 developed by forming indentations 47,49 in an additive layer 51 disposed upon one of the first or second major surfaces 44a,44b of the chip 10. The complementary portion 26 would then be projections from the housing 12, rather than the recesses 50,52 that are described above, to closely mate with the indentations in the additive layer. The additive layer 51 could also be formed into an asymmetrical shape, such as the polygon in FIG. 3, that would be used to locate and orient the chip 10. These configurations have the advantage of providing a larger pad on the chip which would provide a stronger bond to the major surface. Individual semiconductor chips 10 are constructed from larger semiconductor wafers 54 (FIG. 4) through conventional techniques. As shown in FIG. 4, it is possible to produce a number of individual semiconductor chips 10 from a single wafer 54. As used herein, semiconductor chips 10 include integrated circuits, semiconductor lasers, light emitting diodes and any other semiconductor device that has features incorporated during the processing of the semiconductor chip 10 that must be accurately aligned to an externally positioned components. As the wafer 54 is being processed, conductive pads 56, typically 10·16x10 -3 cm (4 mils) by 10·16x10 -3 cm (4 mils) (1 mil = 1 x 10 -3 inches) in size, are deposited upon the wafer 54 in the locations required to establish electrical connection with each of the respective chips 10 being created. The wafer 54 is coated with a passivation layer 58 that protects the processed chip 10 by growing silicon dioxide thereupon or by the deposition of a glass on the wafer 54 (FIG. 5). The passivation layer 58 is chemically etched through at the location of each of the conductive pads 56 to create the contact site 20. The contact site 20 presents an approximately a 2 mil by 2 mil window in the passivation layer 58 for the feet 28 of the connection members 18 to be exposed for electrical engagement in order to establish electrical connection with the semiconductor chip 10. Once the passivation layer 58 has been formed, a photocurable material 60 is placed upon the wafer 54 (FIG. 6). This photocurable material 60 may be the same as what is used as a solder mask in processing printed circuits and typically takes on the form of a thin sheet. One example of this photocurable material is RISTON, a product of E. I. Dupont of Wilmington, Delaware, which is cross-links upon exposure to ultra-violet light. This material may be hot-rolled upon the semiconductor chip. A mask 62 that is preformed to have openings 64 that correspond to the shape of locating members 22, is positioned upon the photocurable material 60 upon the semiconductor wafer 54 in a predetermined orientation to the contact sites 20 and is precisely positioned with reference thereto (FIG. 7). Mask 62 is optically opaque to light of the wavelengths to which the photocurable material is sensitive. The mask 62 is positioned upon the wafer through conventional positioning techniques used in the processing of semiconductor wafers. In this embodiment, the openings 64 would be circular and sized to correspond to the large diameter post 46 and the small diameter post 48 that form the locating member 22. Other shapes may easily be formed in the mask if desired. The photocurable material 60 is exposed through the openings 64 in the mask 62. The exposed portion is illuminated with light having a wavelength that cures the photocurable material 60 in the form of the locating member 22. The mask 62 is then removed and the portions of the photocurable material 60 that were not subjected to illumination, because the mask blocked the light, are washed from the wafer 54 by conventional developing wash solvents leaving behind the now-cured locating members 22 (FIG. 8). The locating members 22 that remain upon the semiconductor chip 10 are precisely located relative the contact sites 20 due to the precise positioning of the mask 62 upon the wafer 54. Once the locating members 22 have been formed upon the semiconductor chips 10 of the semiconductor wafer 54, the wafer 54 may be diced into the individual semiconductor chips 10. The dicing no longer has to be as precise as any deviation from the optimum cutting path, shown as horizontal lines 66 and vertical lines 68 in FIG. 4, no longer effect the positioning of the contact sites 20. The semiconductor chip 10 is located by perimeter independent means that are precisely related to the contact sites 20 of the chip 10.

Claims: A semiconductor chip (10) having contact sites (20) for establishing an electrical connection therewith, the semiconductor chip being receivable upon a housing (12) having connection members (18) correspondingly arranged to at least some of the contact sites (20), so that when the semiconductor chip (10) is received by the housing (12) the connection members (18) electrically engage their respective contact sites (20); wherein; a locating member (22) is disposed upon the semiconductor chip (10) along a major surface thereof and within the perimeter (24) of the semiconductor chip and at a specific position relative the contact sites (20), the locating member (22) being matable with a complementary member (26) of the housing (12) such that when so mated, the contact sites (20) are aligned with their corresponding connection members (18); characterized in that the locating member (22) comprises photocured material upon the semiconductor chip. A semiconductor chip as claimed in claim 1, wherein the locating member (22) has a polarizing configuration, whereby the locating member (22) may only be mated to the complementary portion (26) when the chip is particularly oriented so that respective contact sites (20) and connection members (18) are in a corresponding relationship. A semiconductor chip as claimed in claim 1, wherein the locating member (22) is a pair of cylindrical bosses (48,49) having different diameters. A method of making a perimeter independent precision locating member for a semiconductor chip (10) that ensures that contact sites of a semiconductor chip (10) electrically engage the connection members (28) of a housing (12) when the chip (10) and the locating member (22) are received by a complementary portion (26) of the housing (12); the method comprising the steps of:- (a) depositing a layer of photocurable material (60) upon the semiconductor chip (10); (b) determining the location of the contact sites upon the semiconductor chip; (c) photocuring in precise relationship to the contact sites (20), a portion of the layer (60) deposited upon the semiconductor chip that corresponds to the locating member (22); and (d) stripping the uncured position of the layer (60) from the semiconductor chip, thereby leaving the cured locating member (22) upon the semiconductor chip (10) in said precise relationship to the contact sites (20). A method as claimed in claim 4, wherein the steps (a) and (b) are reversed. A method as claimed in claim 4, wherein the steps (a) through (d) occur while the semiconductor chip (10) is part of a semiconductor wafer (54) and, further including the step of: (f) dicing the individual semiconductor chip (10) from the semiconductor wafer (54). A method as claimed in claim 4, 5 or 6, wherein after determining the location of the contact sites (20), the method further includes the step of masking the semiconductor chip with an optically opaque material (62) having openings (64) in relation to the location of the contact sites (20) so that the locating member (22) is exposed through the openings and the photocuring step is accomplished by illuminating the exposed portion of the layer of material that corresponds to the locating member (22). A method as claimed in claim 7, wherein the stripping of the uncured portion of the layer of material is accomplished by washing away the uncured layer with a solvent.

Inventors: GRABBE DIMITRY G, GRABBE,DIMITRY G.
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1994
Main classification: H01L21
IPC codes: H01L23, H01L21